1. Field of the Invention
The invention relates to a process for preparing a sulfided hydrotreating catalyst, and the use of said catalyst in hydrotreating a hydrocarbon feed.
2. Prior Art
In general, the object of catalytically hydrotreating hydrocarbon-containing feeds is the complete or partial removal of impurities. Common impurities are sulfur compounds and nitrogen compounds. At least the partial removal of such impurities from a feed will ensure that, when the final product is burnt, fewer sulfur oxides and/or nitrogen oxides harmful to the environment will be released. In addition, a reduced content of impurities leads to an improvement of the colour, smell, and stability of the final product. Further, sulfur compounds and nitrogen compounds are toxic to many of the catalysts employed in the oil industry for converting feeds into ready-for-use products. Examples of such catalysts include cracking catalysts, hydrocracking catalysts, and reforming catalysts. It is therefore customary for feeds to be subjected to a catalytic hydrotreatment prior to their being processed in, say, a cracking unit. Catalytic hydrotreatment implies contacting a feed with hydrogen at elevated temperature and pressure in the presence of a hydrotreating catalyst. In this process at least a portion of the sulfur compounds and the nitrogen compounds present in the feed is converted into readily removable hydrogensulfide and ammonia. This is commonly referred to as hydrodesulfurisation and hydrodenitrogenation, respectively.
In general, hydrotreating catalysts are composed of a carrier with a Group VIB metal component and a Group VIII non-noble metal component deposited thereon. The most commonly employed Group VIB metals are molybdenum and tungsten, while cobalt and nickel are the conventional Group VIII non-noble metals. Phosphorus may also be present in the catalyst. The prior art processes for preparing these catalysts are characterised in that a carrier is composited with hydrogenation metal components, for example by impregnation, after which the composite is calcined to convert the metal components into their oxides. Subsequently, the calcined catalysts generally are subjected to a sulfidation treatment.
Because the requirements as to the legally permitted sulfur and nitrogen contents in fuels are becoming ever stricter, there is a continuous need for hydrotreating catalysts with improved activity. Further, at a given final sulfur content of the fuel a more active catalyst will make it possible to operate under milder process conditions (energy saving) or to increase the life span of a catalyst between regenerations (cycle length) or to achieve higher throughput.
Various efforts have been made in the, art to provide hydrotreating catalysts with improved activity. A relatively new trend in this field is the use of organic compounds. For example, WO 95/31280 describes a process which comprises
(i) wetting a catalyst composition comprising a hydrogenation metal by contact with an organic compound such as EDTA,
(ii) ageing the wetted substrate while wet,
(iii) drying the aged substrate, and
(iv) calcining the dried substrate.
It is explicitly disclosed in WO 95/31280 that the drying and calcination steps are carried but in such a way as to remove or decompose the entire amount of organic compound originally present in the hydrotreating catalyst. The resulting hydrotreating catalyst, which consequently does not contain any organic compound, is subsequently contacted with a feed to be hydrodesulfurised, and sulfided in the process.
EP 0164162 also deals with the use of organic compounds in catalyst preparation. However, as in the case of WO 95/31280, a calcination step subsequent to the incorporation of the organic compound into the carrier is described as essential.
WO 96/41848 and EP 0601722 describe processes for the preparation of organic compound-containing hydrotreating catalysts which are used, and thus sulfided, while containing the organic compound. A further reference in which the sulfidation of organic compound-containing hydrotreating catalysts is described is EP0181035.
Comparative Example 1 of EP 0 482 818 describes a catalyst consisting of analumina hydrate carrier containing 22 wt. % of molybdenum, calculated as trioxide, 4 wt. % of cobalt, calculated as oxide, 3 wt. % of phosphorus, calculated as P205, and EDTA in a molar amount of 0.6 times the total molar amount of the Group VI and Group VIII metals. This reference actually claims a method of making a catalyst composition comprising analumina hydrate, a Group VI metal, a Group VIII metal, and a hydroxycarboxylic acid, with the above-cited example merely being comparative.
In one embodiment, the present invention is a process for preparing a sulfided hydrotreating catalyst in which a hydrotreating catalyst is subjected to a sulfidation step. The hydrotreating catalyst comprises a carrier comprising at least 50 wt % of alumina. The catalyst also comprises at least one hydrogenation metal component and an organic compound comprising at least one covalently bonded nitrogen atom and at least one carbonyl moiety. The molar ratio between the organic compound and the total hydrogenation metal content is at least 0.01:1.
It is an important proviso to the above embodiment that the hydrotreating catalyst is not a catalyst consisting of an alumina hydrate carrier containing 22 wt. % of molybdenum, calculated as trioxide, 4 wt. % of cobalt, calculated as oxide, 3 wt. % of phosphorus, calculated as P205, and EDTA in a molar amount of 0.6 times the total molar amount of the Group VI and Group VIII metals. This proviso serves to distinguish that embodiment from the inadvertent disclosure of Comparative Example 1 of EP 0 482 818.
In a second embodiment, the present invention is a process for preparing a sulfided hydrotreating catalyst in which a hydrotreating catalyst is subjected to a sulfidation step. The hydrotreating catalyst comprises a carrier comprising at least 50 wt % of alumina, at least one hydrogenation metal component of Group VI, nickel as an additional hydrogenation metal component, and an organic compound comprising at least one covalently bonded nitrogen atom and at least one carbonyl moiety. The molar ratio between the organic compound and the total hydrogenation metal component content is at least 0.01:1.
In a third embodiment, the present invention is a process for preparing a sulfided hydrotreating catalyst in which a hydrotreating catalyst is subjected to an ex situ sulfidation step, wherein the hydrotreating catalyst comprises a carrier comprising at least 50wt % of alumina. The catalyst comprises at least one hydrogenation metal component and an organic compound comprising at least one covalently bonded nitrogen atom and at least one carbonyl moiety. The molar ratio between the organic compound and the total hydrogenation metal content is at least 0.01:1.
In a fourth embodiment, the present invention is a process for preparing a sulfided hydrotreating catalyst in which a hydrotreating catalyst is subjected to a sufidation step, wherein the hydrotreating catalyst comprises a carrier comprising at least 50 wt % of a transition alumina, at least one hydrogenation metal component and an organic compound comprising at least one covalently bonded nitrogen atom and at least one carbonyl moiety. The molar ratio between the organic compound and the total hydrogenation metal content is at least 0.01:1.
In a fifth embodiment, the present invention is a process for preparing a sufided hydrotreating catalyst in which a hydrotreating catalyst is subjected to a sulfidation step, wherein the hydrotreating catalyst comprises a carrier comprising at least 50 wt % of an alumina, at least one hydrogenation metal component and an organic compound comprising at least one covalently bonded nitrogen atom and at least one carbonyl moiety. The molar ratio between the organic compound and the total hydrogenation metal content is between 0.01:1 and 0.55:1.
Other embodiments of the invention encompass details about the sulfidation step, the organic compound composition, preparation of the catalyst, a process for hydrotreating a hydrocarbon feed wherein a hydrocarbon feed is contacted under hydrotreating conditions with the above-described hydrotreating catalyst, etc., all, of which are hereinafter disclosed in the following discussion of each of the facets of the present invention.